Open blend file like txt file
Blender has a fairly complex system of storing its data using (RNA and DNA). It also stores a vast set of different types of data (colors, textures, assets, images, fonts, objects, modifiers, settings,...). I'd like to think of a blend file as a zip archive with a nested set of directories and files underneath it. But it isn't actually a zip.
What kind of data are you exactly looking for? Lets assume that you are looking for the shape of the objects inside of a blend file. then you could make a python scripts that goes through all objects of bpy.data.objects as ob for instance. You could then find the geometry the object is composed by using ob.data which usually will result in an entry from bpy.data.meshes.
You can than use this to dump its vertices: How to iterate through all vertices of an object that contains multiple meshes?